The invention relates to an electric drive unit for a bicycle.
Such devices have been disclosed in FR 875 752 and in FR 878 837 for example. Internal combustion engines are used to that effect. The disadvantage thereof is that they cannot be switched on and off during the ride, since an internal combustion engine always has to be started first. This occasions unnecessary noise and fuel consumption. Additionally, abrupt stopping often kills the engine. These applications suggest using chain drives. The drawback of a chain drive however is that it has to be lubricated and that the parts used are of metal, which makes them considerably heavier than if they were made of plastic for example. Moreover, the small chain drive wheel cannot be as small as a toothed belt pulley.
Furthermore, these well-known drives cannot be mounted on all customarily employed bicycles. The application FR 878 837 cannot, indeed, be mounted on bicycles styled for girls or women, since the upper crossbar would be in the way. The device disclosed in FR 875 752 requires a radical alteration of the way of driving, since the center of gravity is shifted well rearward, or, if this drive is mounted on a modern, light bicycle, such as a mountain bike for example, there is the risk that the bicycle turns over upon dismounting.
Similar drives have been disclosed in GB 2 164 615 A and U.S. Pat. No. 4,267,898. In these units, the drive pulleys are not affixed to the spokes of the bicycle, so that, as a result, such a drive pulley is more solid and has to be of a heavier design since it cannot rest on the spokes. Additionally, they can only be attached with the help of auxiliary parts. These drives use fanbelts or V belts that have the disadvantage of a certain slip, wherein said slip may become a problem, especially in wet weather.
All these prior-art devices are very heavy and big in size and hence more expensive than they would be if they were small and of a simpler design.
The object of the present invention is to provide an extremely simple, light, ecological and inexpensive auxiliary drive for all customarily employed bicycles. Furthermore, the transmission of the torque onto the bicycle""s wheel should not slip and be maintenance-free and the driving behavior should not noticeably worsen.
According to the invention, the auxiliary drive employs a toothed belt. The drive gear of the belt may be of a much smaller size than the drive gear of a chain drive gear. Accordingly, my device permits a greater gear reduction ratio. As a result, an extremely small, light and inexpensive electric motor may be employed, preferably one with a planetary gear seat flanged thereon. Such a motor is known from modern drilling machines operated on battery for example. By means of a simple clamping holder, this very small geared motor can be directly attached, without disturbing, to various places on the bicycle""s frame, on the support tube for example. The device can thereby be designed to drive the front wheel and/or the rear wheel of the bicycle. When using a great sheave, the forces occurring, like, e.g., the pulling force of the belt, are extremely small, so that the dimensions of the attachment means for the motor can be extremely small and light. Moreover, an extremely inexpensive plastic disk may be used for the sheave, said plastic disk remaining light even if its dimensions are greater to meet a greater gear reduction ratio. Since the sheave on the belt supporting ring is directly attached to the inner side of the wheel spokes, the torque is transmitted to the bicycle""s wheel and, additionally, the sheave is supported by the spokes. The spokes also prevent the toothed belt from running off inside.
This sheave, which has a relatively great diameter, is simply centered for concentricity with the axle of the wheel by positioning it onto the bicycle""s wheel. This is no problem with bicycle wheels that have an outer hub collar, surrounding the central opening of the sheave. This outer hub collar however is missing on most of the new bicycle wheels. For these, the sheave is therefore provided with centering pins arranged in a centric manner around the center, said pins projecting between the spokes and sitting close to the outer periphery of the hub flange.
The sheave is also provided on its outer periphery with a collar intended to prevent the belt from running off, which is well possible due to bumps during the ride.
With only one collar, the sheave may be manufactured with a circumferential toothed bearing surface for the belt by means of an injection die that is very simple in construction. This device permits a great gear reduction ratio onto the drive wheel that is extremely reasonably priced and that does not slip.
To attach the sheave onto the spokes, cable connectors are preferably employed. The sheave may thus be positioned in a very short period of time even by laymen. To attach the sheave, a centrical ring of openings having various outlines may be provided, said openings being arranged relative to the wheel spokes in a way such that the cable connectors are guided through two openings each in order to loop the spokes positioned therein between.
Another object of the invention is not to be detrimental to the usual chain drive with hub clutch or derailleur and to permit the drive to occur ad lib by physical strength and/or by electric drive with a minimum of frictional losses.
To fit this purpose a sleeve type free-wheeling is provided between the drive shaft of the motor or geared motor and the drive wheel, which is carried and runs thereon. As a result, the drive shaft and the drive wheel are connected to rotate in unison by means of clamps when the motor is driving. The freewheeling spins when there is no drive.
A fastener with a location hole that may be attached to a tubular frame member is provided for fastening the geared motor or the electric motor so that the belt may be put under tension or slackened, a protruding threaded stem arranged eccentric to the drive shaft of the motor or geared motor engaging said location hole and being fastened with a screw nut. Once the nut has been slacked and the motor or the geared motor has been turned about its axis, the belt may be put under tension or slackened. Thanks to this way of fastening, the belt may very easily be put under tension even after a change of tire.
The belt may be taken off the drive wheel so that any friction whatsoever that might be occasioned by the belt is excluded during transmission of the torque. In order to attach the detached toothed belt onto the sheave on the bicycle""s wheel, the sheave is preferably provided with pilot pins projecting between the spokes onto which the toothed belt is fixed by forming a loop. This possibility reduces frictional loss to zero and the tire may be changed just as easily as without additional drive. Transmission of the torque to the driven wheel of the bicycle may thus be established and removed again in a fast manner that does not imply any complicated measure.